The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to the use of heavy halogens for enhanced facet etching during the manufacture of semiconductor devices.
Ion bombardment preferentially removes surfaces at an angle to the direction of the ion bombardment, as compared to surfaces normal to the direction of the ion bombardment. For example, the rate of removal of a surface at 45xc2x0 to the ion bombardment direction, (xe2x80x9ccorner sputter ratexe2x80x9d), can be as high as four times the rate of removal of a normal surface (xe2x80x9cnormal sputter ratexe2x80x9d). This effect has found use in the manufacture of semiconductor devices in the form of facet etching, in which upper corners of raised structures on a surface of a semiconductor substrate are preferentially etched by ion bombardment to form xe2x80x9cfacetsxe2x80x9d at such corners. Some of the material sputtered from the facets redeposits at or near the lower portions of the raised structures, resulting in the creation of a prograde profile on the raised structures. Beneficial effects of a prograde profile include increased process yields through improved elimination of stringers, an increased ability to employ highly directional and highly selective processes when depositing and etching between said raised structures, and a decrease in the required amount of over-etch to prevent stringer formation.
The above advantages of facet etching can be enhanced if the ratio of the corner sputter rate to the normal sputter rate can be increased beyond 4:1. This is especially true as feature sizes decrease, which in turn increases the probability of etching through a layer at a normal surface, thereby damaging the underlying structure.
An object of the present invention is provide a method for facet etching,which method provides an increase in the ratio of the corner sputter rate to the normal sputter rate.
Another object of the present invention is to provide a method for facet etching) which method provides a decrease in the normal sputter rate to near zero.
Still another object of the present invention is to provide a method for facet etching, which method provides an increase in the redeposition rate of material sputtered from facets.
In accordance with the method of the present invention, facet etching of a layer to be etched is performed in an inert gas plasma including therein a small amount of a heavy halogen, such as iodine or bromine. The heavy halogen, in the form of ions that are ionized by the plasma and halogen molecules, has the effect of bonding with the material of the layer to be etched, and decreasing the normal sputter rate relative to the corner sputter rate. The redeposition rate of material sputtered from the corners is also enhanced. A small amount of oxygen may also be included in the plasma to enhance the above effects.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.